Automatic Transmission Fluid??? 2000 4Runner 2.7 LI

My 2000 4runner calls for Dexron II; which has been superceded by newer types of Dexron ATF (III).

My question is, can I use something higher rated than Dexron III or should I just stick with the Dexron III. **The reason I want to know is that I am having a really hard time trying to locate the Dexron III ATF. I've gone to 5 Kragen/Autozones and they did not have Dexron III in stock and they did not know when they were getting more.

I called Toyota and they said to use Dexron III. Toyota sells and uses Castrol Dexron III ATF when they do flushes on older model toyotas that require Dexron II(toyota does not make/market their own Dexron III) but they sell it for $7.50 a quart, compared to $3.49 at my local auto parts stores.

If I should only use Dexron III then I am just going to wait and see if I can find it somewhere else at a cheaper price. There is no way I am paying the "stealership" $7.50 a quart for Castrol ATF.

Thanks.